Supported metallocene catalysts are used in many polymerization systems. These catalyst systems typically contain one or more unsubstituted or substituted cyclopentadienyl rings in combination with a transition metal. Usually an activator, such as an alumoxane or an ionizing activator, completes the system. Typically, one or more catalyst system components is supported on a porous support such as silica. Supporting the catalyst improves the handling characteristics of the polymer product and gives better control of reaction rates.
One of the major problems of polymerization using supported metallocene catalyst systems is a phenomenon known as fouling. Fouling occurs when fines within the reactor accumulate and cling to the walls of the reactor or other components of the polymerization system. These particles continue to polymerize and eventually fuse together and form coatings and/or chunks which can interfere with reactor operations such as polymer discharge and heat transfer.
A number of methods have been proposed to alleviate or eliminate reactor fouling. U.S. Pat. No. 5,332,706 describes a method of forming a supported metallocene catalyst using an incipient impregnation technique wherein a very small volume of solution is mixed with a silica support (also see U.S. patent application Ser. Nos. 265,533, filed Jun. 24, 1994 now abandoned and 265,532, filed Jun. 24, 1994, now abandoned herein fully incorporated by reference.) We have discovered that one problem with techniques such as this, where a smaller, controlled volume of liquid is added to a larger volume of dry solid, is that by pouring the solution over the support or using the traditional batch or dropwise manner, localized areas of overwetting may occur particularly when the catalyst is prepared on a large scale. We believe that this localized wetting and uneven distribution of the catalyst system on the silica contributes to fouling during polymerization. Thus, a method that would enable even distribution of the catalyst system on the support that would work on a large scale and that would reduce fouling during polymerization would be highly desirable.